Lyric discussion by Drywid 

Cover art for It's The Fear lyrics by Within Temptation

This song, in line with several others (Overcome, Deceiver of Fools, etc..) is meant to sound pseudo-Christian. "That one day will come to light" is a direct quote from the Bible, "And one day, all sins will come to light." Her fears or 'sins' are consuming her (I feel that I am losing the struggle within... ) and she knows that one day all of her sins will be lain bare.

Choose to take it however you like, of course.

My Interpretation

Not only is there that, there is also the fear that those sins, whatever they may be, will consume her, and destroy her. Thus, they will 'come to light', and become more than just voices in her head.